aggregate_column

# File activerecord/lib/active_record/relation/calculations.rb, line 220
      def aggregate_column(column_name)
        return column_name if Arel::Expressions === column_name

        if @klass.has_attribute?(column_name.to_s) || @klass.attribute_alias?(column_name.to_s)
          @klass.arel_attribute(column_name)
        else
          Arel.sql(column_name == :all ? "*" : column_name.to_s)
        end
      end